Data Visualization Foundations: Mapping Flow Data

After points and area data in maps comes flow data, let's show how our data is connected.

Earlier I’ve talked about how you can visualize point and area data on a map. For this post, I will take it one step further and explain how you
can visualize flow between your points and areas.

When it comes to visualization, it’s always good to look at
what’s been done previously before starting out with something new. For flow data
on a map, my main inspiration is Charles Joseph Minard and his work; namely Napoleon’s Russian Campaign of 1812, but also the map above
showing the export of wine from France. It’s interesting to see how the wine
literally flows out of France towards the different areas of the world, as well
as the complimentary line chart showing the volume.

Flow

To create flows across a map, you need to start with defining
a start position and an end position. This normally points data on your map
and if you don’t have points, you can use the trick from my previous post to
create points from areas. So, if there is a flow between for example countries, you can use the center location of the country as the start/end point. In this
case I’m showing some airline routes to and from Orlando.

Just showing what locations are connected is a good start, but most often you want to add in an amount with your flow. In this case, I can add the number of flights on each route to see which ones are more popular. Then, I also want to split the routes into two and see if the amount of flights to and from are the same. This, I can indicate with a symbol on top of the line to show which direction the flow is going. Since the routes are on the same position on the map, I can add a curvature to the routes to make sure the from and to routes do not sit on top of each other

Lastly, I can also add colors to the lines. In this case, I will add the airlines I’m visualizing and
therefore, I will go with nominal colors to indicate that each airline is
unique.

As you can see, working flows can be interesting and potentially reveal new patterns in your data. Especially, if you work within logistics and want to know your transportation flow.

This is the end to my mapping blog posts for now. Next up, I’ll be blogging about how to visualize distributions!